Using a 4-Wire TPS In A 1G N/T Throttle Body

1G N/T throttle bodies have a larger bore than 2G throttle bodies. The difficulty in swapping these into a 2G is that the 1G TB uses a 3-wire TPS with a separate idle switch, while the 2G uses a 4-wire TPS with the ECU performing the idle switch commands.

The 1G electrical idle switch [edited for accuracy] senses when the throttle plate closes telling the ECU to increase the idle speed under certain engine loads, including AC on, but it also is used when the driver lifts off the throttle completely, preventing the engine from suddenly air starving and abruptly slowing down the car.

The 2G has this function built into the TPS, taking the input from the 4th wire of the TPS and signaling the ECU to activate the ICS motor to compensate in order to produce the correct idle and throttle lift duties.

When converting to a 1G throttle body, you can either keep the 1G idle switch installed with a rewire of the TPS leads to activate the separate idle switch, or, you can install a 4-wire TPS onto the 1G throttle body and replace the idle switch with an idle set screw and locknut.

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When you install the 4-wire TPS on the 1G throttle body, you have to check the continuity on Pins 3 & 4 to make sure they disconnect when the throttle plate is closed. This loss of continuity will signal the ECU to activate the ISC motor.

The problem comes when you check and realize that there is not enough adjustment in the rotational slots of the 4-wire TPS to reach the needed disconnection point at idle.

Here is the way we solved this problem. We bought neodymium magnets -- extremely strong -- to provide a shimmed surface to move the 4-wire TPS into adjustment range so that it could be set to lose continuity at the idle position.

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The magnets were placed on the contact surfaces for the TPS

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They were epoxied into place so they wouldn't shift positions. Once the epoxy set, the 4-wire TPS was installed, ready to be calibrated.

The idle set screw was set to stop the throttle plate from closing to the point where it was sticking when opening. Then the TPS was adjusted to lose continuity on Pins 3& 4 in the idle position.

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Back on the car, the TPS was further adjusted to set the voltage at .42v. There are several good articles on this forum to help you properly set your TPS.

With the throttle body installed and the ISC and TPS plugged back in, it looks clean, with no rewiring needed. This is a great time to install a new ISC motor as well since its proper operation is critical to idle, load compensation and lift throttle operation.

 

[steve]

I think there is some confusion here. Hopefully this will clear it up. If you need more background check the 1G and 2G Technical manuals the the sections in the FSM.

The difficulty in swapping these into a 2G is that the 1G TB uses a 3-wire TPS with a separate idle switch, while the 2G uses a 4-wire TPS with the ECU performing the idle switch commands.

Not accurate. The switches are different but on both 1G and 2G's the Idle Position Switch tells the ECU when the throttle is closed. The ECU's perform various functions based on that input. Either ECU can function with either type switch if adjusted correctly.

The 1G electrical idle switch physically opens the throttle plate for increasing the idle speed under certain engine loads, including AC on, but it also is used when the driver lifts off the throttle completely, preventing the engine from suddenly air starving and abruptly slowing down the car.

Again, not accurate. The 1G IPS doesn't open the throttle plate. It tells the ECU the throttle is closed and the ECU controls the ISC to manage the engine RPM.

When the IPS is closed and the AC pressure switch or the PS pressure switches are active the ECU raises the idle speed by opening up the ISC bypass. When the IPS is open the ECU adjusts the ISC position relative to how much the throttle is open to allow the ECU to emulate a dashpot when the throttle closes to keep the engine from stalling.

The 2G has this function built into the ECU, taking the input from the 4th wire of the TPS and signaling the ICS motor to compensate in order to produce the correct idle and throttle lift duties.

The only difference here is the type of IPS used not what the ECU does in reaction to the input. Both 1G and 2G ECU do similar things to manage idle speed and keep the engine from stalling under deceleration or load.

Then the TPS was adjusted to lose continuity on Pins 3 & 4 in the idle position.

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Back on the car, the TPS was further adjusted to set the voltage at .42v. There are several good articles on this forum to help you properly set your TPS.

Performing this last adjustment effectively negates the prior adjustment of where the IPS opens and closes. The 2G specification provides a range of voltage that is acceptable at idle. As long as your voltage is within the range and the IPS is switching correctly as you begin to open the throttle it's adjusted correctly. If it doesn't there is an issue with the TPS or the circuit it's part of. (like a bad sensor ground or low sensor +5v).

 

[DogWhistle]

Seems our mistake was misunderstanding that the 1G IPS functioned as a dashpot. That has been corrected in the text.

Let’s not lose sight of the purpose of the article: To adapt a 2G 4-wire TPS into a 1G N/T TB.

As you’ve previously stated, 2G owners can keep their 1G TPS if they choose to:

The IPS is inside the TPS on a 2G not external like on a 1G.

Running a 1G TB gives you a bit of a choice, you can use the 2G TPS, keep the factory wiring, and adjust the TPS position based on where the IPS switches like you would with a 2G TB or you can pill the wire for pin 3 on the 2G TPS connector and extend it to connect to the 1G IPS and just set the TPS (either 1G or 2G) by it's output voltage.

What you can't do is use 1 1G TPS without making a provision for the IPS.

This article is for those that choose to update their TPS to the 4-wire style.

Performing this last adjustment effectively negates the prior adjustment of where the IPS opens and closes. The 2G specification provides a range of voltage that is acceptable at idle. As long as your voltage is within the range and the IPS is switching correctly as you begin to open the throttle it's adjusted correctly. If it doesn't there is an issue with the TPS or the circuit it's part of. (like a bad sensor ground or low sensor +5v).

Not in our case. The 2G TPS provides for a voltage range of .4 -1v, and we adjusted the TPS without changing the loss of continuity positioning at idle.

Hopefully all of this discussion will help others understand the critical operation of the TPS functions and how it relates to their engine performance.

 

[steve]

Not in our case. The 2G TPS provides for a voltage range of .4 -1v, and we adjusted the TPS without changing the loss of continuity positioning at idle.

How? The Idle Position Switch is connected to the same shaft as the potentiometer inside the TPS. Any rotation of the body for adjustment effects both. While there is a bit of leeway for adjustment as to when the switch changes state before it becomes an issue for the ECU the factory specification is precise as to how far the throttle should move before the switching should happen. On a DSM (1G or 2G) TPS voltage is a secondary input. The ECU is more interested in the change in position than in absolute.

I wonder at times if the lower voltage limit isn't to avoid physical issues with passing 5v across the low resistance of the TPS at idle. I'm sure the ECU has a high impedance on the TPS input (too lazy to calculate it) but there is some current being passed and across a low resistance means higher power dissipation across that part of the TPS that you see at larger throttle openings.

The interesting part of this article is that you found/concluded that the engagement arms of the 1G NT TB don't provide enough range to adjust a 2G TPS. That's going to require some additional investigation.